FF-P-386 Cotter Pins (Split)

FF-P-386 cotter pins, frequently referred to as split cotter pins, are manufactured from semi-circular cross-section wire formed into two legs joined at a rounded or looped head. They are designed to be inserted directly through a cross-drilled hole in a bolt, castle nut, clevis pin, or rotational shaft. Once properly seated, the two legs are bent apart to mechanically lock the fastener assembly against loosening.

These Federal Specification fasteners are among the most trusted mechanical locking mechanisms in heavy industry. Unlike prevailing-torque nuts or chemical threadlockers that rely strictly on friction, split cotter pins provide a purely physical block against rotation. This makes them a mandatory solution for high-vibration, safety-critical joints like aerospace landing gear or heavy machinery linkages. For detailed part numbers and official documentation, users can search the Defense Logistics Agency (DLA) ASSIST portal.

When installing split cotter pins, mechanical best practices dictate that the pin should fit snugly within the drilled hole of the bolt or clevis pin to prevent rattling. Once inserted, the two legs must be bent apart—typically with one leg folded tightly back over the end of the bolt and the other leg bent downwards against the flat of the nut.

Crucially, because the bending process places severe fatigue on the metal wire, split cotter pins are strictly single-use items. They should never be straightened and reused during maintenance or inspection operations, as repeated yielding of the metal dramatically increases the risk of sheer failure in the field.